The c-abl gene is the cellular homolog of the transforming component (v-abl) of Abelson Murine leukemia virus. In an effort to understand the molecular mechanisms involved in the activation of this oncogene, we and others have recently cloned and sequenced the proviral genome of Abelson virus as well as the c-abl-specific c-DNA clones. These experiments revealed that the c-abl gene codes for multiple transcripts that differ both at the 5' end as well as at the 3' end. The v-abl gene (coding for p120) appears to have arisen from c-abl as result of an extensive deletional process where both 5' as well as internal sequences are lost. In a proto-type virus coding for p160, an identical 5' deletion was observed. In addition, a frame shift mutation was observed in the region that has been deleted from the p120 region, suggesting that changes in this region may also be essential for the oncogenic activity of the transforming gene. In addition to the murine system, rearrangements in the c-abl locus have been observed in human chronic myelogenous leukemias positive for Philadelphia chromosome. Oncogenic activation of the c-abl gene in these human tumors has been found to be associated with 5' deletions where a potion of the c-abl coding region is replaced by a new set of sequences termed bcr. However, unlike in the murine system no internal mutations or deletions have been observed in the human CML tumors. Recent studies indicate that the bcr-abl gene product is a less potent transforming agent that the viral gag-abl fusion product. The present proposal is aimed at addressing the role of deletions and mutations in the activation of the abl proto-oncogene. We propose to construct recombinants between cellular abl gene and its transforming counterparts to assess the role of mutations and deletions in the oncogenic activation of this gene. To understand the effect of these deletions and mutations on the biochemical activity of the proteins, both the transforming and normal proteins will be produced in milligram quantities using eukaryotic expression vectors. Following the purification of the recombinant proteins, we propose to carry out experiments aimed at understanding the biochemical differences between normal and transforming abl proteins.